@@ -63,9 +63,13 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc,
unsigned int fragsz, gfp_t gfp_mask,
unsigned int align_mask)
{
+#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
+ unsigned int size = nc->size;
+#else
unsigned int size = PAGE_SIZE;
+#endif
+ unsigned int offset;
struct page *page;
- int offset;
if (unlikely(!nc->va)) {
refill:
@@ -85,11 +89,24 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc,
/* reset page count bias and offset to start of new frag */
nc->pfmemalloc = page_is_pfmemalloc(page);
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
- nc->offset = size;
+ nc->offset = 0;
}
- offset = nc->offset - fragsz;
- if (unlikely(offset < 0)) {
+ offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask);
+ if (unlikely(offset + fragsz > size)) {
+ if (unlikely(fragsz > PAGE_SIZE)) {
+ /*
+ * The caller is trying to allocate a fragment
+ * with fragsz > PAGE_SIZE but the cache isn't big
+ * enough to satisfy the request, this may
+ * happen in low memory conditions.
+ * We don't release the cache page because
+ * it could make memory pressure worse
+ * so we simply return NULL here.
+ */
+ return NULL;
+ }
+
page = virt_to_page(nc->va);
if (!page_ref_sub_and_test(page, nc->pagecnt_bias))
@@ -100,33 +117,16 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc,
goto refill;
}
-#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
- /* if size can vary use size else just use PAGE_SIZE */
- size = nc->size;
-#endif
/* OK, page count is 0, we can safely set it */
set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1);
/* reset page count bias and offset to start of new frag */
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
- offset = size - fragsz;
- if (unlikely(offset < 0)) {
- /*
- * The caller is trying to allocate a fragment
- * with fragsz > PAGE_SIZE but the cache isn't big
- * enough to satisfy the request, this may
- * happen in low memory conditions.
- * We don't release the cache page because
- * it could make memory pressure worse
- * so we simply return NULL here.
- */
- return NULL;
- }
+ offset = 0;
}
nc->pagecnt_bias--;
- offset &= align_mask;
- nc->offset = offset;
+ nc->offset = offset + fragsz;
return nc->va + offset;
}
We are about to use page_frag_alloc_*() API to not just allocate memory for skb->data, but also use them to do the memory allocation for skb frag too. Currently the implementation of page_frag in mm subsystem is running the offset as a countdown rather than count-up value, there may have several advantages to that as mentioned in [1], but it may have some disadvantages, for example, it may disable skb frag coalescing and more correct cache prefetching We have a trade-off to make in order to have a unified implementation and API for page_frag, so use a initial zero offset in this patch, and the following patch will try to make some optimization to avoid the disadvantages as much as possible. 1. https://lore.kernel.org/all/f4abe71b3439b39d17a6fb2d410180f367cadf5c.camel@gmail.com/ CC: Alexander Duyck <alexander.duyck@gmail.com> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> --- mm/page_frag_cache.c | 46 ++++++++++++++++++++++---------------------- 1 file changed, 23 insertions(+), 23 deletions(-)